Application of numerical simulations are desired to improve the quality of powder products and to optimize the production process in powder die-filling. In the powder die-filling, complex gassolid interaction should be simulated since solid particles are significantly influenced by gas flow under moving wall boundary. The discrete element method (DEM) coupled with computational fluid dynamics (CFD) has been widely utilized in the simulation of gas-solid flows, and the adequacy has been proved through countless studies. On the other hand, the existing DEM-CFD method is extremely difficult to simulate the gas-solid flow where the wall boundary is moving.Besides, in the existing DEM-CFD method, huge number of computational particles cannot be simulated on a single PC. Hence, numerical simulations of the industrial powder die-filling becomes a challenging topic from a viewpoint of evolution of the DEM-CFD method, because modeling of the moving wall boundary as well as modeling of large number of computational particles should be considered simultaneously. Very recently, the authors' group has developed the Integrated DEM-CFD method including the arbitrary shape wall boundary model and the scaling law model. In the Integrated DEM-CFD method, the wall boundary is modeled by the signed distance functions and the immersed boundary method, and besides the coarse graining DEM is employed as the scaling law model. Adequacy of the Integrated DEM-CFD method has been proved through verification tests. In the current study, applicability of the Integrated DEM-CFD method is examined in the powder die-filling. Adequacy of the Integrated DEM-CFD method is shown by agreement between the original particle system and the coarse graining particle system in the powder die-filling. Through the verification tests, macroscopic characteristics of the powder die-filling are shown to be in good agreement between the original system and the coarse grain model system. Consequently, the Integrated DEM-CFD method is illustrated to be effective for the simulation of the industrial powder die-filling systems.

Abstract. This paper presents an analytical study of the correlation between viscosity and fiber diameter in electrospinning. Control over fiber diameter in electrospinning process was important since it will determine the performance of resulting nanofiber. Theoretically, fiber diameter was determined by surface tension, solution concentration, flow rate, and electric current. But experimentally it had been proven that significantly viscosity had an influence to fiber diameter. Jet radius equation in electrospinning process was divided into three areas: near the nozzle, far from the nozzle, and at jet terminal. There was no correlation between these equations. Superposition of exponential series model provides the equations combined into one, thus the entire of working parameters on electrospinning take a contribution to fiber diameter. This method yields the value of solution viscosity has a linear relation to jet radius. However, this method works only for low viscosity.

An angle of repose is defined as the steepest angle of a conical pile that is naturally formed when a bulk of particulate solid is poured onto a flat surface. It has been considered as one of the important properties in characterizing granular material due to its effectiveness in determining flowability of granular, pile profile in an opaque container, and granular transportation system. Since the angle of repose is sensitive to the shape of individual particles, investigations through experiments and simulations for various forms of particles have been carried out. However, most of them were performed under homogeneous particle systems. While in practical situations, granular mixtures consisting of a variety of particle shapes are commonly employed. This study presents an experimental investigation of angles of repose resulting from a mixture of two types of non-spherical particles with different values of roundness. Experiments have been carried out with different compositions and have been repeated five times to ensure their reproducibility. The results show that the angle of repose linearly corresponds to the granular composition, where the coefficient of determination is ~0.95. Therefore, the effect of granular composition in binary mixtures on the characteristics of the resulting pile has been demonstrated in this study.

An electrified nickel wire can produce heat. The heat is transferred to the environment around the wire radiation. However, the temperature produced by the wire will differ depending on the number of voltages supplied by the power source. Here, we do an experiment to measure the temperature of stand-up wire at each voltage of 4.5 V, 6.0 V, 7.5 V, 9.0 V, and 12 V. As a comparison, numerical measurements are done by JavaScript program. We show that the highest temperature of the wire approaches 314 K at 12 V. To equalize the temperature in both methods, the numerical scale factor of time and current in numerical measurements are changed according to the voltage. As a result, temperatures produced in both methods have minimal gap difference with error percentage below 0.5%. In conclusion, the experiment results were used to determine the scaling parameters to approach the ideal thermal response curve in actual values.

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